Try these two things:
1. In
virtualdub disable audio playback [ Audio > (uncheck) Enable audio playback ]
2. In
virtualdub select [ Video> Preview ] and [ Video > Preview acceleration > Off ]
Be sure the video source is playing and you can see it in the virtualdub window, before beginning capture.
If that works you will be capturing audio with video even if you can't hear the audio.
Audio playback during capture while pulling both audio and video over a USB2.0 port can cause the behavior your seeing.. quite often in fact.
Normally you set your audio "Levels" before capture, then turn off audio playback while capturing.
If you want to monitor the audio during playback, put a splitter before the audio jacks are plugged into the 710 jacks and tap the audio for monitoring over headphones there.
Or you can turn on the [Audio > Volume meter] and watch a Level meter real time
You might also be interested to turn on the [Capture > Timing graph] to see how much the system is being overloaded while audio playback is on during USB capture. The gyrating Yellow dots are how overloaded the system becomes trying to wrestle the PCM audio. That's not good.
When audio playback is turned off during capture.. the yellow dots will fall in line and stick strictly in sync with the video.
bonus tip:
USB3.0 ports are scum
If your using a laptop, usually the upper Right side has a pure USB2.0 Standards Compliant port.
The USB3.0 spec de-standardized (unregulated) what it means to be USB3.0 and manufacturers went wild with quality.. not in a good way. Backwards compatibility with USB2.0 devices was totally (optional).. guess what. Manufacturers took that literally for the most part and blaimed the spec if your still using USB2.0 devices.. lol
example: (no kidding) I have an ASUS motherboard with two USB3.0 ports on the backside, labeled (For MASS Storage Devices ONLY!!) the manual for the motherboard says no keyboards, webcams or any non-mass storage device will work when plugged into the USB3.0 ports. They .. sorta.. kinda do.. but break, short out.. and don't live long. Out of frustration I went through the manual one day and discovered the warning labels.
The USB2.0 spec was harsh, draconian, and to the point.. to get the badge manufacturers had to play ball. Those same manufacturers made sure the next spec was "manufacturer friendly" and open to interpretation. ¯\_(ツ)_/¯